next/dist/server/app-render/cache-signal.js

The React Framework

/**
 * This class is used to detect when all cache reads for a given render are settled.
 * We do this to allow for cache warming the prerender without having to continue rendering
 * the remainder of the page. This feature is really only useful when the dynamicIO flag is on
 * and should only be used in codepaths gated with this feature.
 */ "use strict";
Object.defineProperty(exports, "__esModule", {
    value: true
});
Object.defineProperty(exports, "CacheSignal", {
    enumerable: true,
    get: function() {
        return CacheSignal;
    }
});
class CacheSignal {
    constructor(){
        this.count = 0;
        this.earlyListeners = [];
        this.listeners = [];
        this.tickPending = false;
        this.taskPending = false;
    }
    noMorePendingCaches() {
        if (!this.tickPending) {
            this.tickPending = true;
            process.nextTick(()=>{
                this.tickPending = false;
                if (this.count === 0) {
                    for(let i = 0; i < this.earlyListeners.length; i++){
                        this.earlyListeners[i]();
                    }
                    this.earlyListeners.length = 0;
                }
            });
        }
        if (!this.taskPending) {
            this.taskPending = true;
            setTimeout(()=>{
                this.taskPending = false;
                if (this.count === 0) {
                    for(let i = 0; i < this.listeners.length; i++){
                        this.listeners[i]();
                    }
                    this.listeners.length = 0;
                }
            }, 0);
        }
    }
    /**
   * This promise waits until there are no more in progress cache reads but no later.
   * This allows for adding more cache reads after to delay cacheReady.
   */ inputReady() {
        return new Promise((resolve)=>{
            this.earlyListeners.push(resolve);
            if (this.count === 0) {
                this.noMorePendingCaches();
            }
        });
    }
    /**
   * If there are inflight cache reads this Promise can resolve in a microtask however
   * if there are no inflight cache reads then we wait at least one task to allow initial
   * cache reads to be initiated.
   */ cacheReady() {
        return new Promise((resolve)=>{
            this.listeners.push(resolve);
            if (this.count === 0) {
                this.noMorePendingCaches();
            }
        });
    }
    beginRead() {
        this.count++;
    }
    endRead() {
        // If this is the last read we need to wait a task before we can claim the cache is settled.
        // The cache read will likely ping a Server Component which can read from the cache again and this
        // will play out in a microtask so we need to only resolve pending listeners if we're still at 0
        // after at least one task.
        // We only want one task scheduled at a time so when we hit count 1 we don't decrement the counter immediately.
        // If intervening reads happen before the scheduled task runs they will never observe count 1 preventing reentrency
        this.count--;
        if (this.count === 0) {
            this.noMorePendingCaches();
        }
    }
}

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